The New York hedge-fund tycoon — whose disastrous 2011 hire of Ron Johnson as Penney’s CEO has left the retailer in tatters — has lost his sway over the company’s board, which has instead thrown its support behind new CEO Mike Ullman, sources told The Post.

Ackman’s isolation was evident last month when the moneyman tried and failed to quickly replace Ullman, who was tapped for the top job after being ousted by Ackman ahead of the Johnson hire, according to insiders close to the company.

Ackman insisted to investors and business associates in April that Ullman was merely warming the chair on an interim basis. He interviewed a handful of retail superstars to finish cleaning up Johnson’s mess, according to insiders.

Ken Hicks, a former top exec at Penney who is now CEO of Foot Locker, was among the execs approached by Ackman, sources said.

Jerry Storch, who announced in February he will step down from a seven-year stint as CEO of Toys R Us, was also approached, these sources added.

Ackman even offered the CEO job to Allen Questrom, the legendary merchant who headed Penney from 1999 to 2004, one insider said. Questrom turned him down.

“Apart from stabilizing the company, finding a permanent CEO [was Ackman’s] top priority,” a source said.

Nevertheless, the silver-haired hedgie’s frenzied search to replace Ullman quickly tapered off as it became clear that Penney’s board wasn’t interested, sources said.

Ackman had hoped to replace Ullman within three to 12 months, sources said. But Ullman — Ackman’s bitter nemesis since the two clashed beginning in 2010 during Ullman’s first CEO stint — has lately signaled that he intends to remain CEO for the foreseeable future, sources said.

“Really, you could say the struggle [between Ackman and Ullman] was mostly in Bill’s mind, because he had no leverage after Johnson left,” said one person close to the retailer. “[Ackman] has lost all credibility as a retail genius.”

The big chill must have blown in quickly.

In recent weeks, Ackman played a key role in securing for Penney a $1.75 billion loan from Goldman Sachs, backed by its real estate, sources said. Blackstone Group, the longtime investment banker for Ackman’s fund, Pershing Square Capital Management, helped broker the deal.

Ackman declined to comment yesterday.

Hicks couldn’t immediately be reached for comment, while Storch and Questrom both declined to comment, as did Penney officials.

Johnson, a former Apple exec, was ousted April 8 after his disastrous bid to eliminate coupons and discounting sent sales plunging 25 percent last year, fueling a loss of nearly $1 billion.

Despite his rift with the board, Ackman is sticking with his 18-percent stake in Penney and doesn’t plan to interfere as Ullman gears up for the crucial back-to-school and holiday seasons, according to an insider close to the situation.